Geographic Range

The northern boundary of the distribution of Saccopteryx bilineata occurs in central Mexico, with capture records from Jalisco and Veracruz. The range extends south to central South America including northern Bolivia, Guyana, Suriname, Guyane, and eastern Brazil, but excluding Paraguay. The range of Saccopteryx bilineata extends as far south as Rio de Janeiro on the eastern coast of South America. Saccopteryx bilineata has also been found on Antillean islands, including Trinidad and Tobago. (Jones and Hood, 1993; Yancey, et al., 1998)

Habitat

Saccopteryx bilineata is found throughout lowland neotropical forests, but it also makes use of man-made structures and can be found in disturbed habitats and plantations. Most specimens have been found near water sources. This species roosts under bridges, in caves, in cliff crevices, and in hollow trees. Saccopteryx bilineata has been recorded roosting with many other bat species; however, it tends to roost in more well-lit places than most other bats. (Jones and Hood, 1993; Tuttle, 1970; Yancey, et al., 1998)

Physical Description

Saccopteryx bilineata has dark pelage with 2 whitish longitudinal stripes running down the dorsal side of the body from each shoulder to the rump. This species has a simple muzzle without a leaf-like nasal structure or inflation of the rostrum. The black color of S. bilineata fades to deep brown as it becomes worn. The ventral surface is brown to gray. The uropatagium is slightly hairy. Total length varies from 73 to 78 mm, the length of the tail is on average 21.6 mm, the length of the ear ranges between 17.51 and 17.96 mm, and the length of the forearm is between 47.13 and 49.16 mm. Saccopteryx bilineata body mass ranges from 8.5 to 9.3 g, females are generally slightly larger than males.
The skull has a large post-orbital process and premaxillilaries that are incomplete and not attached medially. This species has 32 teeth with a dental formula of 1/3, 1/1, 2/2, 3/3. Cranial length ranges from 13.2 to 15.7 mm.
The dorsal stripes are pronounced in S. bilineata and serve as a distinguishing feature when comparing this bat to Saccopteryx canescens. Saccopteryx bilineata is larger and has a darker pelage than Saccopteryx leptura, which is lighter brown. As with all members of this genus, this species has wing sacs which help to distinguish it from superficially similar bats of the genus Rhynchonycteris. (Eisenberg, 1989; Genoud and Bonaccorso, 1986; Yancey, et al., 1998)

Reproduction

The Saccopteryx bilineata mating system is polygynous, in which males defend harems of 3 to 5 females from other males. Since females are larger than males, they control copulation and are often more agonistic toward males than accepting. Therefore, males principally maintain a roosting and foraging territory in order to attract females. Males also use a suite of olfactory, visual, and ultrasonic vocal displays to attract and retain females. Males spend much of the afternoon cleaning the sacs on their wing membranes with saliva and urine. A genital secretion is then collected with the chin and applied to the wing sacs. Once the sacs are prepared, a male performs flight displays in which it hovers over females in the harem and flaps its sacs toward her in a behavior known as “salting.” Typically, salting is reserved for visiting females outside of the harem, whereas established females receive a hovering display and courtship song which may go on, intermittently, for one hour. A female usually responds by flying away or swatting at the male with her wing (80% of copulation attempts); or she may reciprocate with a less complex social call that is often a precursor to copulation. Harem size is positively correlated with song complexity (number of syllables in a song), as well as with frequency of male displays. Additionally, molecular studies have verified that male reproductive success is positively correlated with harem size. (Voight, et al., 2006)

A single male guards the harem from non-harem males both at the roost and when the harem forages at night. A male may use a short territorial song to ward off other males, and antagonistic encounters between males are resolved after a brief barking match. However, within a harem, cryptic males wait to usurp the harem if the harem male is removed. Based on removal studies, the succession of harem males by cryptic males depends on tenure within the colony; cryptic males that have been in a harem the longest take over the harem. This suggests a seniority-based hierarchy among males and may be one reason why males are highly philopatric, in hopes that their fidelity to the harem will eventually result in access to the females. (Voight, et al., 2006)

Researchers have also observed a social hierarchy in the females of a harem. A female that consistently wins dyadic interactions against other females tends to position herself in the warmest area of the roost, highest from the ground. These females experience fewer copulation attempts from the harem male and tend to change roosts less often than females of a lesser rank. They also try to drive off females looking to join the harem, but will relent if a new female is persistent. Harem fidelity is relatively low among females, with one study finding that 60% of females visit at least 3 harems per day. Visiting females receive a majority of the copulation attempts and harassment from harem males. (Voight, et al., 2006)

Although males work to maintain a harem throughout the year, females are typically receptive to copulation once a year. In Costa Rica, females allow males to breed with them during an approximate four week period in December and January, which coincides with the end of the seasonal rains. During the breeding season, a male’s testes swell to 0.2% of his body mass. Fertilization and implantation occurs soon after copulation, and a fetus is recognizable eight weeks after fertilization. However, fetal development slows dramatically at this point, since gestation lasts six months. (Bradbury and Vehrencamp, 1977; Voight, et al., 2006; Yancey, et al., 1998)

In Costa Rica, births occur in a three week span from May to June with pregnant females in a colony undergoing synchronous parturition. This period is generally the onset of the rainy season, but in years where the rains are delayed, a stressed female is able to resorb or abort a pregnancy. Successful pregnancies result in a single newborn that is fully furred, weighs 40% of its mother’s mass, and has a forearm length that is 60% of the adult forearm length. As the offspring mature, 75% of males stay in the colony while all females leave. Of females that leave, 16% go on to inhabit a neighboring colony, whereas the outcome of the other 84% is unknown. (Bradbury and Vehrencamp, 1977; Voight, et al., 2006; Yancey, et al., 1998)

Breeding season lasts for about 4 weeks between December and January (at the conclusion of the rainy season).

Average number of offspring

1

Average gestation period

6 months

Average weaning age

2 months

Average time to independence

2 months

Average age at sexual or reproductive maturity (female)

12 months

Range age at sexual or reproductive maturity (male)

7 (low) months

Average age at sexual or reproductive maturity (male)

12 months

Only females provide direct parental care. Although they are relatively well developed, newborns cling to their mothers until their first flight 10 to 14 days after birth. Lactation continues for another 6 weeks, at which point juveniles becomes fully independent. Adult males, despite having no direct parental investment, are important in how juveniles learn and practice vocalizations. Using bat detectors, researchers discovered that juveniles appear to mix rudimentary elements of several call types much in the same way many juvenile birds and infant humans babble incoherently when first learning to communicate (only documented case of babbling in a mammalian species outside of primates).

Behavior

Multiple harems of Saccopteryx bilineata combine to form a colony of around 15 bats; an exceptionally large colony may contain around 60 individuals. Within a colony, a harem male defends 1 to 3 sq. meters of the roost and its associated females from other males. Individuals are quite active during the day, always changing roost sites, enticing new females, or maintaining appropriate spacing. Bats at the roost tend to space themselves at least 10 cm apart, which is thought to mitigate predation on a colony. An individual encroaching on the space of another is often met with barking and swatting. Even while foraging at night, females maintain a relatively strict territory. Females forage in an area 10 to 20 meters in length, adjacent to other females in the harem, and chase away non-harem females and smaller insectivorous bat species. The harem male forages the entirety of the territory occupied by his associated females, and defends the territory (ranging from 10 to 30 sq. meters) from other males. These bats forage for 2 to 3 hours before retiring to vegetation within the feeding territory. Females with young either forage while carrying their offspring or drop them off at a nearby roost. (Bradbury and Vehrencamp, 1976; Voight, et al., 2006; Yancey, et al., 1998)

Home Range

Home ranges are variable depending on the status and sex of the bat, but the average home range at La Pacifica study site in Costa Rica was found to be 6.9 hectares. (Bradbury and Vehrencamp, 1976)

Communication and Perception

Like most other bats, greater sac-winged bats use echolocation to perceive their environment and forage. The frequency ranges of their foraging calls are between 42 and 50 kHz. In addition to echolocation vocalizations, S. bilineata males use vocalizations along with olfactory and visual cues to attract mates to their harem. Males perform hovering displays when a female enters their territory and they produce complex songs as both territorial and courtship displays. Territorial song bouts last up to 4 seconds and consist of 20 to 50 elements. These songs are produced occasionally throughout the day and more frequently at dawn and dusk, when the colony is most active. Courtship songs are more complex than territorial songs and may last for minutes or up to an hour. These songs are usually at a frequency of above 20 kHz, with tonal elements known as trills composed of a rippled modulation of the basal frequency modulation. The trill element of the courtship song varies from male to male, suggesting it may play a role in female choice and individual identification. Males also use scents with females, with perfume displays increasing in frequency prior to and during the mating season. Females respond to scent displays with social vocalizations or by waving a folded forearm at the male. Recent chemical analysis by gas chromatography has shown that S. bilineata and its sister species Saccopteryx leptura have species specific male scents. Female choice experiments confirm that females prefer the scent of their own species over those of sister species. (Caspers, et al., 2009; Voight, et al., 2006; Yancey, et al., 1998)

Food Habits

Saccopteryx bilineata is strictly insectivorous. Diet studies in Costa Rica and Trinidad have found S. bilineata consuming primarily beetles and flies whereas other studies have found frequent consumption of lepidopterans. Specialization on one prey type has not been observed. Greater sac-winged bats forage 3 to 8 m from the ground using straight-line chases and sharp turns before obstacles. Foraging occurs for 2 to 3 hours after dusk with 20 to 30 minutes of effort in each foraging bout. Greater sac-winged bats use relatively long, paired search phase calls with the first call lasting 5.1 to 6.7 ms and the second call, 2 to 3 kHz lower, lasting 4.8 to 6.0 ms. Calls are characterized by a slight rise in frequency at the beginning of a pulse, followed by an extended constant frequency portion, ending with a slight decrease in frequency. Calls vary in frequency throughout the geographic range of Saccopteryx bilineata, from 47 to 50 kHz recorded in a Costa Rican population and 43 to 45 kHz documented in a population in Belize. Colonies of S. bilineata have exclusive foraging ranges, with most individuals from one colony sharing a foraging area. Although individuals from a colony forage near each other, they forage in a solitary manner, unlike the group foraging of closely related Saccopteryx leptura. Studies in Costa Rica showed that foraging activity of S. bilineata is positively correlated with phenological activity and presumably insect abundance in forested habitat. Due to the highly seasonal nature of food sources, S. bilineata changes foraging patches every 5 to 10 weeks. (Barclay, 1983; Bradbury and Vehrencamp, 1976; Yancey, et al., 1998)

Predation

No specific data are available on predation of S. bilineata. Possible predators which have been recorded preying on other bat species include snakes, owls, and small carnivores. Greater sac-winged bats are cryptically colored when roosting and are active at night, protecting them from some predation. (Nowak, 1994)

Ecosystem Roles

Greater sac-winged bats are insect predators. If these bats occur in high densities or with many other species, the accumulation of their feces may be a significant source of nutrients to the soil and plants under their roost. They also significantly impact populations of insects and are parasitized by a number of internal and external parasites. (Bradbury and Vehrencamp, 1976)

Commensal/Parasitic Species

streblid flies (Euctenodes) (ectoparasite)

trombiculid mites (Eutrombicula goldii) (ectoparasite)

trombiculid mites (Trombicula saccopteryx) (ectoparasite)

trombiculid mites (Trombicula vesperuginis) (ectoparasite)

Economic Importance for Humans: Positive

Saccopteryx bilineata is the most abundant insectivorous bat species in some regions of the neotropics. Although no specific information is available on the quantity of insects consumed by S. bilineata, it is likely that they play a role in controlling insect populations, as demonstrated in several recent studies of insectivorous bats in the tropics. (Kalka, et al., 2008; Voight, et al., 2006; Williams-Guillen, et al., 2008)

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

polygynous

having more than one female as a mate at one time

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.